A discharge lamp apparatus used as a light source of, for example, a projector and a cinema projector comprises a high pressure discharge lamp, which serves as a light emitting source, and a concave reflection mirror, which surrounds the high pressure discharge lamp. An optical system such as an integrator lens and a reflective mirror, and a spatial modulation element such as a DLP (Registered Trademark) and a liquid crystal panel are provided on a front side thereof in a light emitting direction of the concave reflection mirror, whereby light from the high pressure discharge lamp is emitted onto a screen to project an image on the screen.
In general, a light source, which has emission spectrum excellent in color balance of RGB, is required, to project an image, which is excellent color-reproduction nature on the screen. However since the light intensity of a red component is low in such a high pressure discharge lamp that is formed of an ultrahigh pressure mercury lamp while the light intensity of a green component is relatively high, it does not have the emission spectrum that is excellent in color balance of RGB as a whole, so that when the high pressure discharge lamp is used as a light source, there is a problem that the color-reproduction nature of the image projected on the screen is low.
To solve such a problem, in Japanese Patent Application Publication No. 2004-29267, a discharge lamp apparatus is proposed wherein a laser light source, which emits laser light of a red wavelength band, is provided separately from a high pressure discharge lamp, and the laser light is synthesized with light emitted from the high pressure discharge lamp. In the discharge lamp apparatus, the laser light source is arranged on a front side thereof in a light emitting direction of a concave reflection mirror, and the laser light is synthesized with the light emitted from the high pressure discharge lamp, on an optical path along the central axis (optical axis) of the concave reflection mirror, whereby the laser light, which is red light, is added to the light emitted from the high pressure discharge lamp, so that the light intensity of the red component may be compensated. Therefore, the light source, which has emission spectrum excellent in the color balance of RGB, can be obtained, and when such a light source is used as a light source of a projection type display apparatus, an image with an excellent color-reproduction nature may be projected.
However, since a degree of coherence of light emitted from such a laser light source is high compared with light emitted from such a high pressure discharge lamp, there is a phenomenon called “speckle noise,” that is, a garish flickering on a screen occurs due to interference of the laser light, whereby the quality of an image deteriorates.